CVE-2025-31366
📋 TL;DR
This vulnerability allows unauthenticated attackers to perform reflected cross-site scripting (XSS) attacks against Fortinet FortiOS, FortiProxy, and FortiSASE products via crafted HTTP requests. Attackers can inject malicious scripts that execute in victims' browsers when they visit manipulated URLs. Organizations using affected versions of these Fortinet security products are at risk.
💻 Affected Systems
- Fortinet FortiOS
- Fortinet FortiProxy
- Fortinet FortiSASE
📦 What is this software?
Fortios by Fortinet
Fortios by Fortinet
Fortiproxy by Fortinet
Fortisase by Fortinet
Fortisase by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal session cookies, credentials, or sensitive data from authenticated users, potentially leading to account takeover or data exfiltration.
Likely Case
Attackers craft phishing emails with malicious links that execute scripts in victims' browsers, potentially stealing session information or redirecting to malicious sites.
If Mitigated
With proper input validation and output encoding, malicious scripts are neutralized before reaching users' browsers, preventing successful exploitation.
🎯 Exploit Status
Exploitation requires social engineering to trick users into clicking malicious links. No authentication is required to trigger the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiOS 7.6.4, 7.4.9, and later versions; FortiProxy 7.6.4 and later versions; FortiSASE 25.3 and later versions
Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-24-542
Restart Required: No
Instructions:
1. Log into Fortinet support portal. 2. Download appropriate firmware updates for your affected products. 3. Apply updates following Fortinet's upgrade procedures. 4. Verify the update was successful.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement strict input validation and output encoding for all user-supplied data in web interfaces
Content Security Policy (CSP)
allImplement a strict Content Security Policy header to mitigate XSS impact
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to detect and block XSS payloads
- Educate users about phishing risks and safe browsing practices
🔍 How to Verify
Check if Vulnerable:
Check current firmware version via CLI: 'get system status' or GUI: System > Dashboard > System InformationCheck Version:
get system status | grep VersionVerify Fix Applied:
Verify firmware version is patched: FortiOS 7.6.4+, 7.4.9+, or later versions; FortiProxy 7.6.4+; FortiSASE 25.3+📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests with script tags or JavaScript payloads
- Multiple failed XSS attempts from single IPs
Network Indicators:
- HTTP requests containing suspicious script patterns or encoded payloads
- Unusual redirect patterns in web traffic
SIEM Query:
source="fortigate" AND (http_uri="*<script*" OR http_uri="*javascript:*" OR http_uri="*onload=*" OR http_uri="*onerror=*")